The JSONL backend rethrows storage errno failures and abort signals from the
source read of a pending migration unwrapped; a test now drives both through
the stat seam so the classification stays covered. The navigation-panes Web
e2e derives the exported archive entry from `SESSION_FORMAT_VERSION`, which
`session-log-export` uses for its `session.v<N>.jsonl` name. The module graph
records the `session-log-export` → `session` peer edge.